The embodiments disclosed relate generally to rotating machines with at least a main active magnetic bearing and auxiliary rolling bearings. In particular, the embodiments relate to rotating turbomachines such as compressors, expanders, turbines, pumps, etc. The turbomachines are used in engines, turbines, power generation, cryogenic applications, oil and gas, petrochemical applications, etc.
One turbomachine often used in the industry includes a centrifugal compressor which increases the pressure of a compressible gas through the use of mechanical energy by rotating centrifugal impellers through which the gas passes. The impellers are attached to a compressor shaft. The rotating shaft and the associated impellers form a rotor assembly which is supported in the stator of the compressor by active radial and axial magnetic bearings.
The active magnetic bearings levitate and maintain the rotor assembly in position inside the stator by applying electromagnetic forces on the assembly in axial and radial directions. To this end, the active magnetic bearings comprise electromagnets supplied with electrical energy. With such magnetic bearings, the rotor assembly is held with no mechanical contact. Such a holding necessitates supplying the electromagnets with sufficient electrical power.
Failure or insufficient normal operation of the active magnetic bearings may sometimes occur with an interruption of the electrical power supply. Failure may also occur in the event of excessive loads applied on the rotor assembly.
In these cases, the active magnetic bearings no longer center the rotor assembly inside the stator. Accordingly, there appears a “landing” phase during which the rotor assembly tends to come into contact with the stator and is held with mechanical contact.
To overcome this drawback, the centrifugal compressor further comprises two single row angular contact ball bearings mounted face-to-face on the compressor shaft axially next to the active magnetic bearings. Each auxiliary rolling bearing is provided to support both radial and axial loads when a “landing” phase appears.
However, with such ball bearings, the number of landing phases which can be sustained without any inadmissible changes in clearance dimensions of the bearings is limited. This leads to a reduction of the reliability of the rotating machine and to an increase of the maintenance operations. Besides, for a rotating machine with limited accessibility, costs of such maintenance operations can be extremely high.
An aim of embodiments of the present invention is to overcome these drawbacks.